In some stacked multichip packages (stacked semiconductor devices) in which a plurality of semiconductor elements are stacked and sealed in a package, a semiconductor element larger than a lower-side semiconductor element is stacked on an upper side, or a semiconductor element on an upper side is stacked in an offset manner. In such cases, part of the upper semiconductor element projects from an outer periphery of the lower semiconductor element, and an area under the projecting portion is hollow. If electrode pads provided on the projecting portion of the upper semiconductor element are wire-bonded, a load at this time bends the semiconductor element. Such bending may cause a crack of the semiconductor element or a connection failure of metal wires.
To solve this, it is effective to fill an adhesive bonding the upper semiconductor element to the lower semiconductor element, in the hollow portion under the projecting portion of the upper semiconductor element (see JP-A 2004-158716 (KOKAI) and JP-A 2006-005333 (KOKAI)). Further, there is also an increasing demand for a thinner multichip package. To realize this, it is effective to use an adhesive containing an insulating filler functioning as a spacer. JP-A 2006-005333 (KOKAI) describes that the adhesive containing the insulating filler functioning as the spacer is used, and the adhesive is filled in an area under the projecting portion of the upper semiconductor element while a gap between the upper semiconductor element and the lower semiconductor element is kept narrow.
At this time, by lowering the viscosity of the adhesive made of a thermosetting resin composition or the like, it is possible to uniformly fill the adhesive in the gap between the semiconductor elements, which can realize a stacking structure with a narrow inter-element gap. However, lowering the viscosity of the adhesive may possibly cause the rotation or movement (chip shift) of the upper semiconductor element when the upper semiconductor element is mounted (is pressed) or when the adhesive undergoes a curing process. Increasing the viscosity of the adhesive could prevent the chip shift but would not make it possible to uniformly spread the adhesive in the gap between the semiconductor elements even by the application of a load at the time of the bonding of the upper semiconductor element and to obtain a non-defective thinned package. The viscosity of the adhesive is in a trade-off relation with the reduction in the inter-element gap and the non-defective element stacking structure.
JP-A 2007-324443 (KOKAI) describes that an upper semiconductor element is bonded to a lower semiconductor element by using adhesive resin whose resin property expressed by a product of viscosity and thixotropic ratio is 700 or higher, and the adhesive is filled in a hollow portion under a projecting portion of the upper semiconductor element. Here, in filling the adhesive in the hollow portion under the projecting portion, based on the resin property expressed by the product of viscosity and thixotropic ratio, the adhesive is prevented from flowing out. However, no consideration is given to realizing both the reduction in the inter-element gap and the non-defective element stacking structure.